Evaluation of limited irrigation strategies to improve water use efficiency and wheat yield in the North China Plain

The North China Plain is one of the most important grain production regions in China, but is facing serious water shortages. To achieve a balance between water use and the need for food self-sufficiency, new water efficient irrigation strategies need to be developed that balance water use with farmer net return. The Crop Environment Resource Synthesis Wheat (CERES-Wheat model) was calibrated and evaluated with two years of data which consisted of 3–4 irrigation treatments, and the model was used to investigate long-term winter wheat productivity and water use from irrigation management in the North China Plain. The calibrated model simulated accurately above-ground biomass, grain yield and evapotranspiration of winter wheat in response to irrigation management. The calibrated model was then run using weather data from 1994–2016 in order to evaluate different irrigation strategies. The simulated results using historical weather data showed that grain yield and water use was sensitive to different irrigation strategies including amounts and dates of irrigation applications. The model simulated the highest yield when irrigation was applied at jointing (T9) in normal and dry rainfall years, and gave the highest simulated yields for irrigation at double ridge (T8) in wet years. A single simulated irrigation at jointing (T9) produced yields that were 88% compared to using a double irrigation treatment at T1 and T9 in wet years, 86% of that in normal years, and 91% of that in dry years. A single irrigation at jointing or double ridge produced higher water use efficiency because it obtained higher evapotranspiration. The simulated farmer irrigation practices produced the highest yield and net income. When the cost of water was taken into account, limited irrigation was found to be more profitable based on assumptions about future water costs. In order to increase farmer income, a subsidy will likely be needed to compensate farmers for yield reductions due to water savings. These results showed that there is a cost to the farmer for water conservation, but limiting irrigation to a single irrigation at jointing would minimize impact on farmer net return in North China Plain.华北平原是中国最重要的粮食主产区之一，却面临极为严峻的水资源短缺困境。为实现水资源利用与粮食自给需求间的平衡，亟需开发新型节水灌溉策略，在合理管控用水的同时保障农户净收益。本研究采用包含3~4组灌溉处理的两年实测数据，对作物环境资源综合小麦模型（Crop Environment Resource Synthesis Wheat, CERES-Wheat）进行率定与验证，并借助该模型探究华北平原长期冬小麦生产能力与灌溉管理模式下的用水情况。率定后的模型可精准模拟不同灌溉管理措施下冬小麦的地上生物量、籽粒产量与蒸散发量。随后研究使用1994-2016年的气象数据运行该率定模型，以评估不同灌溉策略的应用效果。基于历史气象数据的模拟结果显示，籽粒产量与用水量对包括灌溉总量与灌溉时期在内的各类灌溉策略均表现出显著敏感性。模拟结果表明，平水年与干旱年在拔节期（T9）进行灌溉可获得最高籽粒产量，而湿润年则在双棱期（T8）灌溉时模拟产量最高。在湿润年，仅在拔节期（T9）单次灌溉的籽粒产量仅为T1与T9两次灌溉处理的88%；平水年该比例为86%；干旱年则可达91%。仅在拔节期或双棱期进行单次灌溉可获得更高的水分利用效率，因其可提升作物蒸散发量。模拟的农户常规灌溉模式可实现最高产量与净收益。若将水资源成本纳入考量范畴，结合未来水资源成本的假设前提，有限灌溉方案的盈利性更为突出。为提升农户收入，或需出台补贴政策以弥补农户因节水减产带来的收益损失。上述研究结果表明，水资源保护对农户而言存在一定的成本代价，但将灌溉限制为拔节期单次灌溉，可将其对华北平原农户净收益的负面影响降至最低。